Nonmagnetic Elinvar-Type Alloys in Mn-Ni System

Abstract

Measurements of Young’s modulus and thermal expansion at −150°∼400°C, and of rigidity modulus and hardness at room temperature have been carried out with Mn-Ni alloys subject to various heat-treatments and cold-works. It has been found that Mn-10.15∼35.30%Ni alloys slow-cooled after heating at 950°C for 1 hr had clear minimum or maximum in Young’s modulus-temperature curves, and there anomalies correspond to antiferromagnetic Néel points or fcc\ ightleftarrowsfct martensitic transformation. The values of Young’s modulus at room temperature did not show a great difference among the annealed state, the cold-worked state, the reheated state after cold-working, the water-quenched state and the reheated state after water-quenching, but the difference being large in the γ phase and the mixture phase on the Mn side. Besides, a large minimum value of Young’s modulus was recognized near 18.5% of nickel contents. The temperature coefficient of Young’s modulus at room temperature was affected largely by heat-treatment, cold-working and alloy composition, and the temperature coefficient vs. composition curves exhibit a large maxima and minima in positive and negative signs. The highest positive temperature coefficient of Young’s modulus in the annealed state is +119.50×10⁻⁵ for the alloy containing 20.30%Ni, thus showing the Elinvar property. Further, the variation in rigidity modulus and its temperature coefficient by heat treatment, cold-working and alloy composition bears a close resemblance to that in Young’s modulus and its temperature coefficient. The hardness in the annealed state, the water-quenched state and the reheated state after water-quenching was generally lower than that in the cold-worked state and reheated state after cold-working.